Abstract:

Water pollution is a serious global environmental challenge. It has been estimated that approximately 20% of industrial water pollution is related to the use of synthetic dyes in the food, cosmetic, pharmaceutical, textile and leather industries.¹ Synthetic dyes market comprises more than 10,000 different types of dyes and pigments with an annual production of around 0.8 million tons.² Azo dyes are the most important class of synthetic dyes and make up 70-75% of the organic dyes annually produced.³ Owing to inefficient binding of dyes to different substrates, about 10-15% of dyes are released to the environment every year during the dyeing and finishing process.² These synthetic dyes are not only toxic and carcinogenic to human health but also negatively affect the natural aquatic systems by hindering the light available for photosynthesis. In addition, presence of these dyes in natural water bodies alter their pH and chemical oxygen demand.⁴ It has been reported that traditional wastewater treatment methods, such as activated sludge treatment process, are not effective in removing azo dyes and their corresponding breakdown products.⁵

Oxygen (O₂) dark activation is a promising method for the degradation of azo dyes. It involves the generation of reactive oxygen species from oxygen present in wastewater that subsequently led to the formation of radicals for the degradation of dyes. This process accelerates in the presence of a catalyst which acts as a bridge for electron transfer between the dye and reactive oxygen species. Surface properties and oxygen vacancies of the catalyst play a key role in the generation of reactive oxygen species. Importantly, O₂ dark activation does not require the use of additional reagents or even the presence of light. In this work, we have tested a series of perovskite-type oxides for the catalytic degradation of azo dyes under dark conditions. These oxides were synthesized using a citrate-based sol-gel method and characterized using powder x-ray diffraction and N2 physisorption analysis. Degradation studies of different dyes were performed in a batch reactor at different temperatures and concentrations and monitored by the UV-Vis absorption spectroscopy. Among the synthesized catalysts, SrFeO_3-∂ showed a degradation efficiency of ~88% for methyl orange under dark conditions at room temperature (25°C).

Thesis Committee

• Dr. Qasim Imtiaz (supervisor)
• Dr. Ali Rauf (thesis committee member/evaluator)
• Dr. Falak Sher (thesis committee member/evaluator)